Multiscale computational analysis of the effect of end group modification on PM6:BTP-x OSCs performance

Abstract

The active layer morphology of organic solar cells (OSCs) plays a crucial role in achieving high PCE. Nevertheless, conventional experimental techniques struggle to dynamically observe the evolving morphology of the active layer in OSCs at the atomic scale and obtain electronic structure information, which limits the rational design of photovoltaic materials. In this work, we employed a combined method of Ab initio molecular dynamics (AIMD) simulations and density functional theory (DFT) calculations to obtain information on the molecular stacking structure and excited states of donor/acceptor (D/A) dimers at the D/A interface of the PM6:BTP-x (x = eC9, S9, and S14) systems, and to further explore the charge transfer mechanism. The AIMD results indicated that the stacking style, orientation and distance between D/A molecules significantly affect the charge transfer and charge separation. In addition, fluorinated and chlorinated end groups are compared. The chlorinated end group enhances local excitation/charge transfer hybridization, largely reduces the exciton binding energy, and achieves a more balanced hole and electron transfer rate, while the fluorinated end group reduces the intermolecular π–π stacking distance, and is better able to reduce the ΔE_HOMO between D and A. Combined AIMD and DFT approaches were adopted to investigate the intrinsic relationship between the molecular structure and performance of PM6:BTP-x OSCs, and this multiscale approach provides theoretical guidance for designing and developing high performance OSCs.